How to build a movable garden shed base?

nieldy

Hi, I want to install a garden shed (approx 2 X 2 metres) in a location where there is a water pipe and electric/gas lines underground, so I can't dig too deep, and I need it to be movable without a huge amount of effort in the case that something needs to be accessed in the ground. See the area in the photo below...

 

I was thinking of buying this Lifetime shed (Lifetime 2.1 x 2.1 x 2.27m Desert Sand Polyethylene Plastic Garden Shed - Bunnings Australia) because it should be easier to move than a metal or wooden shed.

And, I was thinking of building a wooden shed base, something like this (How to build a floating shed foundation // Great for uneven and flat yards! - plans available!).I Just have a few questions related to the shed base...

* Firstly, does a wood base seem like the best way to go considering my requirement for it to be movable and not require much digging?
* In the video I linked above, the base uses concrete blocks to rest the wood beams on (I know something like TuffBlocks can also be used). I've seen some videos that just have the wood resting directly on the ground with anchor points going into the ground. Just wondering which would be best for my situation. There's a slight slope on the ground, but I think I should be able to level it fairly well.
* Also, in the video he puts floor sheeting (OSB) down on top of the frame. I'm just wondering if I would need floor sheeting given the Lifetime shed will have its own flooring. Or will this help to keep it level or provide better anchor points for the shed floor? Do you have any other suggestions for what to put on top of the frame?
* What timber would you recommend for the wood frame? Would H3 treated pine be ok (i.e. 140 x 45mm Outdoor Framing H3 Treated Pine - 4.8m - Bunnings Australia), or would H4 treated pine be better, or something else?
* Should I put down a gravel or similar base under the timber frame base, or is it ok directly over soil?

Any advice is appreciated,

Cheers,

Stephen

JacobZ

Hi @nieldy,

Thank you for your question about constructing a base for your Lifetime 2.1 x 2.1 x 2.27m Desert Sand Polyethylene Plastic Garden Shed.

I'll start by mentioning that the installation manual for this shed, which contains a guide for constructing a timber shed base, can be found here: Lifetime 7 Ft. x 7 Ft. Outdoor Storage Shed.

In your situation, a timber base is going to be your best option as it will give you a flat, solid foundation to anchor your shed to, while still being movable if required. 
 

The main thing I would be tossing up is whether to have it raised, like in your video or sitting flat on the ground. If it were raised, you would just need to level under the foundation blocks or pedestals, whereas if it were sitting on the ground, you would need to level all the areas where it is in contact with the ground. 

If you were to use a raised base like in the video above, you could use H3 materials, but you would essentially be building a deck, so we should follow the principles of deck building and use the appropriately sized timbers for the spans. In this situation, where you require a 2070mm x 2120mm base (measurements from the manual), you would need to use 140x45 H3 with 3 pedestals per bearer, which would look like this.

While this is an option, I think having your base sit directly on the ground would be a better option because the materials are cheaper, the construction is easier, and anchoring would be simpler. You would just have to put in a bit of extra work to level it out at the beginning, but every other aspect of construction would be simpler as it would be directly supported by the ground all throughout. Being in direct contact with the ground, you would need to use H4-treated timber. I'd suggest using sleepers. You could build essentially the same frame as above using 200mmx50mm sleepers.

As a foundation, I would suggest digging out trenches for the footprint of the frame and adding around 50mm of drainage gravel for both levelling and drainage purposes. Use a tamper to level and compact the gravel to create a solid base.

You could then connect the frame together with landscape screws and attach the frame to the ground using sleeper stakes.

This shed requires support under the entire floor, so you couldn't just leave the frame as is, you would need to add a flat surface to it. Instead of plywood or OSB, which don't usually hold up well where moisture is present, I'd suggest using 90 x 22mm Decking H3 Treated Pine.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob